Has anyone used a GPS to check the speedometer precision?

I found that my speedometer was reading 2-3 mph faster than the GPS speed, and I have heard that the GPS is pretty accurate.

 

Have you changed the size of your wheels and tires? I was told when I upgraded to 17's, that my speedometer would be off my a few miles.

 

I still have the original wheels and tires. I thought it might just be delay from the GPS, but the speedo was definitely reading about 3 mph faster at 60 mph.

 

there was another thread around here not to long ago. They said the same thing.

 

http://forums.bradbarnett.net/showth...ghlight=speedo
I think there's another one out there also.

 

Yep. Same thing. But, when I installed my white faced guages I "fudged" on the reinstall of the needle so it more accurately reflected real world speed.

 

I haven't upgraded anything on my 06 GT. However, it does have factory 18-inch wheels and tires. Should I assume that's why my speedo also seems to read a few mph fast? I've never done a test on it, but I'm like others -- I doubt everybody is driving 75-80 mph.

 

The 18" and 17" wheels have different size tires, making them almost identical in their diameter. They are like 2 revolutions per mile different or something miniscule, not enough to make any difference on the speedo.

 

No, shouldn't matter. I thought maybe you had changed them. Still wouldn't have changed it much per the post above this one. Just threw a question out there. Hope ya figure it out.